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ABSTRACT NO. 0934
PAPER NO. 0372
Corresponding Author:
John
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Novotny
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John
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Novotny
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Upper Extremity
Glenohumeral
Joint Anatomy Animal Model
COMPARATIVE ANATOMY OF THE HUMAN GLENOHUMERAL JOINT TO THREE ANIMAL MODELS
+*Novotny, J.E., Macy, J.C., Nichols, C.E. III, Beynnon, B.D.; +*The University of Vermont, McClure Musculoskeletal Research Center, Dept. of Orthopaedics and
Rehab., Stafford Hall, Burlington, Vermont, USA 05405; PH (802)656-2250; FAX:(802)656-4247; [email protected]
Introduction: Study of injuries to the glenohumeral joint, its capsule and
articular surfaces and their healing responses requires the development of an
adequate animal model. Knowledge of the differences in the anatomy
compared to the human is necessary. There is little known about injury and
healing response of the glenohumeral joint capsule after dislocation. Animal
models have been developed to address these issues in other joint systems.
The rat has been identified as a model of rotator cuff injury [Soslowsky,
1996]. Rabbits have been used in studies of the knee ligaments [Woo, 1992,
Walsh, 1992]. Primate models might be more anatomically accurate for
studying the glenohumeral joint. The objective of this work is to describe the
differences in the glenohumeral joint anatomy of the rat, rabbit and monkey
compared to human. An understanding of the bony, muscular and capsular
anatomy of these animal models will aid in assessing their future usefulness
in the study of human glenohumeral pathology.
Methods: Three common animals used in medical research were studied.
These were the Sprague-Dawley rat (Rattus norvegicus), white New Zealand
rabbit (Oryctolagus cuniculus) and Rhesus monkey (Macaca mullata). Three
other animals were excluded earlier due to growth or gross morphological
differences: chicken, pig and cow. Four specimens of each animal were
dissected with detailed examination of the muscles and soft tissues of the
glenohumeral joint. Photographs were taken at each step of the dissection for
documentation and comparison. The outer layers of skin and fat were
removed. The layers of muscle over the shoulder girdle were dissected from
those near the surface to the rotator cuff. An attempt to identify all human
muscles was made and others were noted. The tendons of the rotator cuff
muscles were separated from the glenohumeral capsule, and thickenings
within the capsule were observed. The glenoid labrum was examined. The
bony and articular surfaces were finally noted after the capsule was removed.
The results note differences of the animal model compared to the human
anatomy.
Results:
Rat:
Bone: The greater tuberosity projects from the shaft by more than
the shaft’s diameter and extends distally. The scapula is more tear-drop
shaped than triangular. The coracoid projects from the scapula adjacent to
the anterior rim of the glenoid. The acromion extends laterally from the
scapular spine.
Muscle: The muscles include all those in the human and also a
dorso-epitrochlearis. This runs from the latissimus dorsi tendon to the distal
humerus. Teres minor is very small in comparison to the other rotator cuff
muscles.
Capsule: The capsule is very thin, almost entirely translucent.
There is a thin anterior band, running from the superior glenoid to the
inferior-medial humeral head similar to the SGHL. There are also thickenings
posterior-inferiorly, perhaps representing an IGHL complex. No
coracohumeral ligament was identified An axillary recess is present. A
labrum is robust and attached firmly to the glenoid rim.
Rabbit:
Bone: The humerus is thick with a prominent greater tuberosity
and deep bicipital groove. The scapula is triangular and the medial-lateral
dimension is twice the superior-inferior. The glenoid face has distinct
superior and inferior facets with the superior facet directed inferiorly. The
facets are not continuous with an obvious transition between them. The
acromion extends inferiorly from the spine of the scapula. The clavicle is not
attached to the acromion.
Muscle: All human muscles are present.
Capsule: There were no real thickenings visible within the
capsule. There was a dense thick intra-articular ligament from the anterior-
superior glenoid to the anterior-medial humeral head distinct from the capsule
consistent with the coracohumeral ligament in the human. There was no
axillary recess or labrum. A rotator interval was present. No coracoacromial
ligament was identified.
Monkey:
Bone: There is less retroversion of the humeral head with respect
to the epicondylar line. The scapula is triangular with the medial-lateral
dimension one and a half that of the superior-inferior. The glenoid is concave
in the supero-inferior dimension with the superior facet angled inferiorly.
There is a prominent supraglenoid tubercle. The coracoid projects inferolaterally. The acromion extends laterally from the scapular spine.
Muscle: All human muscles are present along with three others.
The intraspinatus runs along the distal scapular spine to the greater tuberosity
between the supraspinatus and infraspinatus. The dorso-epitrochlearis is
present as in the rat. The coracobrachialis profundus runs from the tip of the
coracoid to the anterior humerus distal to the lesser tubercle.
Capsule: There is a prominent intra-capsular thickening from the
superior tubercle of the glenoid to the anterior-medial humeral head similar to
the SGHL. Also there is a thickening extending from the superior glenoid to
the medial humeral head, or IGHL. A distinct extra-capsular thickening from
the base of the coracoid to the anterior humeral head is consistent with the
coracohumeral ligament. An axillary recess and rotator interval were also
present, as well as a firmly attached labrum. There is no coracoacromial
ligament.
Discussion:
None of these three models is an ideal representation of the anatomy of the
human glenohumeral joint. The primate and rat have distinct capsular and
glenoid geometries that are nearer to human than the rabbit. None of the
animals have similar scapular geometries and differences in the humerus are
evident. Differences in the acromion and coracoid are also present. Muscular
anatomies are consistent in the rotator cuff for the rat and rabbit, with the
monkey having the additional intraspinatus and coracobrachialis profundus
deeply, and the monkey and rat having the dorso-epitrochlearis nearer to the
surface. Consideration of the more bipedial biomechanics and greater size of
the joint may make the primate model more useful, although practical,
monetary concerns may lead to use of the rat. The many anatomical
differences in the rabbit make it less useful.
Acknowledgments: Bristol-Meyers Zimmer Squibb Excellence in
Orthopaedics Award.
References:
Soslowsky et al.: Development and use of an animal model for investigations
on rotator cuff disease. J Should Elbow Surg 5: 383-392, 1996.
Walsh and Frank: Two methods of ligament injury: a morphological
comparison in a rabbit model. J Surg Res 45: 159-166, 1988.
Woo et al.: Biology, healing and repair of ligaments. In Biology and
Biomechanics of the Traumatized Synovial Joint: the Knee as a Model.:
Editors: Finerman and Noyes. AAOS, Rosemont, IL 1992.
One or more of the authors have received something of value from a commercial or other party related directly or indirectly to the subject of my presentation.
The authors have not received anything of value from a commercial or other party related directly or indirectly to the subject of my presentation.
45th Annual Meeting, Orthopaedic Research Society, February 1-4, 1999, Anaheim, California
372